Metal some electrons are present in the conduc0on

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Unformatted text preview: 0 K •  •  Insulator: no electrons are present in the conduc0on band at T=0 K and the energy gap is large (Eg > ~10 eV). Virtually no electrons can be thermally excited from the valence band to the conduc0on band at T=300 K. Semiconductor: no electrons are present in conduc0on band at T=0 K and the energy gap is smaller (~0.1< Eg < ~5 eV). Some electrons are thermally excited from the valence band to the conduc0on band at T=300 K. Metal: Some electrons are present in the conduc0on band at T=0 K and the conduc0on band is either par0ally filled or overlaps valence band. 11 Electrons and Holes in “Perfect” Semiconductors •  When an electron is freed from the valence band where it was involved in atomic bonding, an empty state is lel behind •  In a perfect, undoped semiconductor, electron- hole pairs can be created through thermal excita[on or by interac[on with a photon •  Once created, the electrons and holes are free to move (dril and diffusion) Light Heat Equa[on for a Parabola y = ax 2 ← Curvature at origin related to "a" coefficient y = 5x2 y = x2 3.2 2.4 1.6 0.8 -4.8 -4 -3.2 -2.4 -1.6 -0.8 0 0.8 1.6 2.4 3.2 4 4.8 -0.8 -1.6 -2.4 15 -3.2 Electrons in Free Space •  As a consequence of wave- par[cle duality, the electron has a wave- like nature p2 Classical Mechanics: E = 2m E ψ ( z, t ) = Ae[ i ( kz−ω t )] 2π where k = (wave vector...
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